The manufacture of polyurethane polymers often requires the production of a polymer having a reduced density to provide suitability and economic viability for the use in certain applications. Polyurethane polymers of reduced density, also referred to as polyurethane foam, are generally prepared by reacting an organic polyisocyanate with a polyether or polyester polyol in the presence of a physical blowing agent. Traditionally the employed blowing agents have been organic substances such as the fully halogenated or "hard" chlorofluorocarbons as exemplified by trichlorofluoromethane. However the continued use of "hard" chlorofluoroalkanes has been restricted by many governmental agencies in the interest of the environment. As an alternative, "soft" chlorofluoroalkanes distinguished by a hydrogen atom content such as, for example, dichorofluoromethane, tetrafluoroethane or chlorofluoromethane, have been proposed. The blowing efficiency of the mentioned alternative substances is frequently inferior to trichlorofluoromethane, and system solubility problems leading to processing complications are often encountered when preparing polyurethane foam. A more recently proposed alternative is the use of aliphatic or alicyclic alkanes and especially n-pentane, isopentane or cyclopentane. However the use of alkanes can also be accompanied by system solubility problems and additionally a flammability risk, unless appropriate precautions are taken. A yet more recent alternative now proposed in many instances is the use of water. Water is a "chemical" blowing agent and provides for a reduced density of the polyurethane polymer by its exothermic reaction with the polyisocyanate leading to the in situ generation of gaseous carbon dioxide which then confers the reduced density to the polymer. The use of water is associated with formation of a polyurea content in the polyurethane polymer and frequently confers an undesirable hardness and brittleness to the foam requiring compensation by selection of polyol or polyisocyanate. Additionally when intending to prepare an integral-skinned polyurethane product it is well recognized that use of water to generate carbon dioxide generally does not provide for an attractive skin formation.
It is now widely accepted that carbon dioxide is to be the blowing agent of choice meeting many of the customer desires and environmental demands. Accordingly, it would be desirable to provide an alternative source of carbon dioxide which is able to minimize the recognized deficiencies of water when producing a polyurethane foam, including an integral-skinned product.
Carbon dioxide can also be generated by thermal decomposition of certain inorganic substances such as ammonium carbonate or ammonium hydrogen carbonate. Organic substances can also be a source of carbon dioxide by their thermal decomposition, exemplary of such substances include carbon dioxide complexes of amines. U.S. Pat. No. 3,425,964 discloses the use of a solid substance, obtained by contacting carbon dioxide with a liquid polyfunctional amine, as curing agent when preparing a polyurethane polymer. DE 21 32 102 discloses the preparation of complexes by contacting carbon dioxide with a low molecular weight polyamine. The patent publication FR 2,121,556 discloses the preparation of a complex from ethanolamine with carbon dioxide and use of the adduct when manufacturing a polyurethane polymer. Similarly, the publication U.S. Pat. No. 5,464,880 discloses the preparation of CFC-free cellular polyurethane polymer in the presence of a complex obtained from an aliphatic aminoalcohol with carbon dioxide. U.S. Pat. Nos. 4,645,630 and 4,499,038 disclose use of amine/carbon dioxide adducts in the manufacture of polyurethane polymers wherein the amine has at least 3 aliphatic ether groups per molecule.
To provide a polyurethane polymer with a commercially attractive reduced density it is necessary to use the above mentioned substances in a relatively large amount to generate the required volume of carbon dioxide; this amount becomes significantly greater with increasing molecular weight of the amine. If polyurethane polymer is prepared in the presence of amines of elevated molecular weight this can significantly change and lead to inferior or undesirable physical properties of a resulting polyurethane polymer. To overcome these deficiencies it would be desirable to provide for an amine/carbon dioxide adduct which is able to release a significantly larger volume of carbon dioxide per part by weight of complex. To facilitate handling it would also be desirable to provide for an amine/carbon dioxide adduct which is liquid at ambient temperature. Further it would be desirable if the use of the complex when manufacturing a polyurethane polymer has the ability to improve the physical properties of the resulting polyurethane polymer.